textproduct: Albany

WHAT HAS CHANGED

No major changes to the forecast.

KEY MESSAGES

1) Scattered showers and thunderstorms develop across eastern NY and western New England today. There is a marginal risk (level 1 of 5) for isolated severe thunderstorms, mainly this afternoon, with damaging winds, frequent lightning and heavy downpours the primary hazards.

2) Isolated to scattered showers and thunderstorms are expected Monday and Tuesday, especially near and north of I-90.

3) Chances of showers and thunderstorms return late next week as temperatures trend warmer.

DISCUSSION

KEY MESSAGE 1...

Latest water vapor imagery shows our parent trough centered just north of the Great Lakes with a secondary shortwave rounding the base through the Ohio Valley. An area of rain and thunderstorms continues to push through PA early this morning ahead of the occluded boundary within a region of diffluent flow downstream of the trough. However, high res and deterministic guidance is in good agreement showing these showers/storms continuing to weaken as they advance north and eastward through sunrise as they outrun the best forcing for ascent. While a few isolated showers develop ahead of the occluded front before sunrise, the weakening area of showers/embedded storms should reach eastern NY and western New England 09 - 15 UTC this morning. The occluded boundary essentially stalls over eastern NY today with the secondary shortwave from the Ohio Valley continuing to rotate into the Northeast, reaching eastern NY by early afternoon. As stronger height falls arrive, expecting scattered clusters of showers/storms to redevelop and track from west to east. Forecast soundings and moisture profiles also show dry air surges into eastern NY/western New England this afternoon as this stronger shortwave arrives. This will help steepen mid- level lapse rates over 6C/km with DCAPE values also rising over 1000 J/kg. The incoming dry air should also help morning stratus break for sun with dew points in the mid to upper 60s supporting sfc-based instability increasing towards 1000 - 1500 J/kg per the REFS and CAMs. Given the incoming closed low, 0-6km shear impressively reaches 40-50kts and 0-3km shear 25-30kts.

Despite these favorable ingredients for severe weather, clouds look to break for sun just as the stronger height falls arrive, limiting the time for the atmosphere to destabilize before convective initiates. In addition, low-level forcing is limited to a weakening warm front lifting northward along a washout occluded front. These help explain why the HREF and REFS both only show low probabilities for updraft helicity values exceeding 20m/s mainly 20 - 00 UTC. This indicates that even as isolated to scattered storm clusters initiate mid to late afternoon into the early evening hours, there should only be isolated instances of severe thunderstorms. Given weak updraft growth, there are also questions if any storms can tap into the stronger shear aloft. This matches with SPC's marginal risk (level 1 of 5) in their Day 1 Convective Outlook. Damaging winds remain the primary hazard from any severe storms that form but any storm can also produce frequent lightning as forecast soundings show sufficient instability extending into the favored -10C to -30C region likely due to the cool/dry air tracking in aloft. Storms can also produce heavy downpours given PWATs over 1". Convection dissipates by 0 - 02 UTC with clouds clearing quickly thereafter, supporting radiational fog overnight where heavy rain fell.

KEY MESSAGE 2...

Our mature closed low slowly propagates into southern Quebec by Monday with its cool pool extending into eastern NY and western New England. Southwest flow aloft will maintain elevated dew points in the mid 50s to low 60s with the 500hPa -15C to -18C cool pool aloft supporting steeper mid-level lapse rates 6 - 6.5C/km with morning sun contributing to SB-CAPE values reaching 500 - 1000 J/kg. As a stronger shortwave rotates around the base of the closed low late Monday morning into the afternoon, stronger forcing for ascent should support a more organized area of rain and even embedded thunderstorms tracking west to east. Given the cool pool, storms will not need to become too tall before lightning develops with any taller updrafts capable of small hail. However, forecast soundings shows low EL heights indicating low-topped convection and thus limiting severe weather potential.

Winds shift westerly by Monday evening in the wake of the shortwave with cool air advection over the still warm lakes supporting a lake effect and upslope rain response. Therefore, we continue to show likely and categorical POPs in the western Adirondacks with chance POPs in the southern Greens and Mohawk Valley. Westerly flow and the trough axis/cool pool under our very slow moving closed low should maintain at least scattered showers during the day on Tuesday favored near and north of I-90. The western Adirondacks and southern Greens will likely receive the highest rainfall amounts. Instability wanes by Tuesday so any storms should be isolated.

KEY MESSAGE 3...

High pressure builds back overhead by Wednesday supporting pleasant and dry conditions. However, the dry break does not last long as yet another shortwave trough approaches the Northeast Thursday into Friday. Southwest flow ahead of it will allow humidity levels to rise once again with temperatures trending slightly above normal. Heights fall in response to the approaching trough and eventual cold front looks to support increased chances for showers and thunderstorms both days. However, there remains uncertainties in timing and coverage of shower/storms as there are discrepancies on the strengthen of the incoming cold front and placement of the parent trough in southern Canada.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

Through 06z Monday...Primarily MVFR conditions prevail across all terminals early this morning as low level moisture continues to increase ahead of an incoming occluded boundary. Over the next several hours, conditions should stay relatively steady, though scattered breaks in cloud coverage could result in some brief improvements in ceilings to VFR heights. Or, in the case of PSF, breaks could result in improvements from IFR to MVFR. Regardless, by about 10-13z, all sites will consistently sport IFR to MVFR conditions as low-level stratus becomes more consistent and showers begin to spread across the region. Rainfall rates in this initial round of rain will be light, so visibility is expected to remain around 4-6SM. A brief break in precipitation then comes late morning into early this afternoon before the potential for scattered thunderstorms increases later this afternoon. As confidence is not high in the exact timing or location of thunderstorms, PROB30s were included in the TAFs to highlight the period of greatest potential. Generally, the greatest probability of thunderstorms lies between 20- 01z. Once these conclude and the aforementioned boundary departs near the end of the 06z TAF cycle, improvements to the VFR category are expected. Winds will begin our of the southeast today at sustained speeds under 10kt. By this afternoon, winds will increase to around 10kt or so before the boundary shifts winds to the west and southwest. Sustained speeds will then fall back under 10 kt by the end of the period.

Outlook...

Monday Night: No Operational Impact. NO SIG WX. Tuesday: Low Operational Impact. Breezy. Slight Chance of SHRA. Tuesday Night: No Operational Impact. NO SIG WX. Wednesday: No Operational Impact. NO SIG WX. Wednesday Night: No Operational Impact. NO SIG WX. Thursday: Moderate Operational Impact. Breezy. Chance of SHRA...TSRA. Thursday Night: High Operational Impact. Likely SHRA...TSRA. Friday: Moderate Operational Impact. Chance of SHRA...TSRA.

ALY WATCHES/WARNINGS/ADVISORIES

CT...None. NY...None. MA...None. VT...None.